1. Field of the Invention
The present invention relates to a base net supporting mechanism for a seat cushion used in a seat structure formed by stretching across a cushioning member over a seat frame and a seat structure containing the base net supporting mechanism for a seat cushion, and in particular relates to a base net supporting mechanism for a seat cushion suitable for a transportation machine such as a plane, a train, a ship, a forklift, a motor vehicle and so on and a seat structure containing the base net supporting mechanism for a seat cushion.
2. Description of the Related Art
A seat structure formed by stretching a cushioning member such as a solid knitted fabric (a three-dimensional net member) across a seat frame is disclosed in Patent Documents 1 to 5. When forming a cushioning member stretching across a seat frame in this manner, in order to enhance preventability of bottom-touch, vibration absorbency, impact absorbency, a base net made of cloth such as a solid knitted fabric, a two-dimensional cloth and the like is provided below the above-described cushioning member via an elastic member. In all of the Patent Documents 1 to 5, a torsion bar unit including a torsion bar, an arm connected to the torsion bar, and rotatably supported by the torsion bar as a fulcrum, and a supporting frame supported by the arm, is disposed in the rear of a seat, and the base net is elastically supported by connecting the rear end of the base net to the supporting frame. Note that the front end of the base net is fixed to a front frame composing the seat frame.
[Patent Document 1] Japanese Patent Application Laid-open 2004-347577
[Patent Document 2] Japanese Patent Application Laid-open 2003-182427
[Patent Document 3] Japanese Patent Application Laid-open 2004-188164
[Patent Document 4] Japanese Patent Application Laid-open 2004-141545
[Patent Document 5] International Patent Publication WO 2004/007238A1
In the technology disclosed in Patent Documents 1 to 5, by elastically supporting a base net with a torsion bar, it is possible to achieve improvement of vibration absorbency as described above without bringing a feeling of something foreign to users despite a fact that by using thinner material compared with urethane material generally used in a prior art as a cushioning member for a car seat or the like, a hip point (H. P.) is lowered by about 10 mm compared with using the urethane urethane. However, in all the technology described above, a torsion bar is disposed in the rear of the seat cushion, and the front end of the base net is fixed. In particular, a structure disposing arms and a supporting frame connected to a torsion bar on the rear tilting upper side is excellent in vibration absorbency, but gives a feeling of the buttocks or the pelvis being pushed from behind when seating due to pulling the rear end of the base net in a rearward and upward-tilting direction, or gives a sense of so-called seating on a hammock. Then, the sense of seating on a hammock is eliminated by taking a countermeasure such as lying urethane material under the buttocks, the urethane material having a thickness of about 20 mm and being enhanced in facial rigidity by impregnating felt into the urethane. Disposition of another urethane material in the front of the seat, and at the same time, disposition of an auxiliary net to prevent forward displacement of the buttocks under the base net are carried out, but it is also necessary to lay still another net or a plastic board or the like between the front urethane and the auxiliary net in order to ensure a supporting surface with no fluctuation in body pressure distribution (surface having a sense of continuous support) because a force to push up from rear by the torsion bar works. Moreover, since the front end is fixed, a force of the leg is received at the time of pedal operation, and the counter force thereof is perceived as a sense of hitting on the front end of the seat. Furthermore, since urethane material used at the front part of the seat has a feeling of springiness relatively hard, it sometimes lacks a sense of stroke.